In my experience, there are very few people that fall between the two. They are either the examples I provided above or they are, like myself, silent until they have something to provide that is of a real contribution and not just "I have a mouth, so I'm going to make stuff come out of it because I can!". So it's either a flood of drivel or a silent vacuum.

I concede that social networks are not 100% noise, but the signal value is so small that I don't see there being enough return for the amount of work needed to whittle it down to mostly 'content'.